A hard contract was signed today for somewhere between $460 million and $465 million; no brokers were involved in the transaction. A source involved in the transaction said that Blackstone Group is one of the potential lenders. A spokeswoman for Blackstone wasn’t immediately available for comment.

The 614,000-square-foot 850 Third Avenue between East 51st and East 52nd Streets was designed by Emery Roth and is currently home to Discovery Communications, which leases roughly 160,000 square feet of space. Other tenants include Shearman & Sterling and Radio One.

Shorenstein picked up the property in 2008 as part of a package along with Park Avenue Tower at 65 East 55th Street between Park and Madison Avenues for $930 million, according to city records.

MHP declined to comment on the deal as did Blackstone. Shorenstein did not return press inquiries by deadline.